Bottom Line:
Bacterial communities were isolated from two different sites of a 13-year experimental field with a clay-silt texture.Plasmid molecules were detected at low frequency (27 isolates, 2%) with a size ranging between 2 Kb and 40 Kb.As it might be expected, even though the viable cells title did not differ significantly between the two samplings, the overall data disclosed an uneven distribution of both species and plasmid-harboring strains.

ABSTRACTIn this work the analysis of the plasmid presence on soil aerobic cultivable heterotrophic bacterial communities was carried out checking a panel of 1,200 isolates, in order to establish the frequency of plasmid presence as well as the degree of plasmid flow between strains affiliated to the same or different taxon. Bacterial communities were isolated from two different sites of a 13-year experimental field with a clay-silt texture. Plasmid molecules were detected at low frequency (27 isolates, 2%) with a size ranging between 2 Kb and 40 Kb. The RAPD analysis performed on the plasmid-harboring isolates and the phylogenetic analysis of the whole community using the 16S rRNA gene sequences revealed the existence of transfer of the same plasmids between strains belonging to the same species and, in some cases, to different species of the same genus. As it might be expected, even though the viable cells title did not differ significantly between the two samplings, the overall data disclosed an uneven distribution of both species and plasmid-harboring strains.

Figure 3: Phylogenetic trees constructed using the 16S rRNA sequences obtained from Stenotrophomonas (A), Enterobacter (B), Paenibacillus(C), and Acinetobacter (D) isolates analyzed in this work and the most similar sequences retrieved from databases. Bootstrap values > 50are shown. The pairwise deletion option was used. Isolates harboring one or more plasmids are marked by a black or white dot or a grey triangle.Isolates harboring a plasmid with the same electrophoretic mobility are marked with the same symbol.

Mentions:
Data reported in Table 4 revealed that bacteria belonging to Stenotrophomonas, Acinetobacter, Enterobacter and Paenibacillus included both isolates harboring or lacking plasmid molecules. To check the existence of a possible correlation between the presence of plasmids and the phylogenetic position of bacterial isolates, a phylogenetic tree for each of these four genera was constructed (Fig. 3), whose analysis revealed that some isolates embedded in the same genus very likely belong to different species, since the sequences joined different clusters of a phylogenetic tree. This is particularly true for Enterobacter and Acinetobacter isolates, whereas Stenotrophomonas and Paenibacillus exhibited a more homogeneous distribution within the respective tree.

Figure 3: Phylogenetic trees constructed using the 16S rRNA sequences obtained from Stenotrophomonas (A), Enterobacter (B), Paenibacillus(C), and Acinetobacter (D) isolates analyzed in this work and the most similar sequences retrieved from databases. Bootstrap values > 50are shown. The pairwise deletion option was used. Isolates harboring one or more plasmids are marked by a black or white dot or a grey triangle.Isolates harboring a plasmid with the same electrophoretic mobility are marked with the same symbol.

Mentions:
Data reported in Table 4 revealed that bacteria belonging to Stenotrophomonas, Acinetobacter, Enterobacter and Paenibacillus included both isolates harboring or lacking plasmid molecules. To check the existence of a possible correlation between the presence of plasmids and the phylogenetic position of bacterial isolates, a phylogenetic tree for each of these four genera was constructed (Fig. 3), whose analysis revealed that some isolates embedded in the same genus very likely belong to different species, since the sequences joined different clusters of a phylogenetic tree. This is particularly true for Enterobacter and Acinetobacter isolates, whereas Stenotrophomonas and Paenibacillus exhibited a more homogeneous distribution within the respective tree.

Bottom Line:
Bacterial communities were isolated from two different sites of a 13-year experimental field with a clay-silt texture.Plasmid molecules were detected at low frequency (27 isolates, 2%) with a size ranging between 2 Kb and 40 Kb.As it might be expected, even though the viable cells title did not differ significantly between the two samplings, the overall data disclosed an uneven distribution of both species and plasmid-harboring strains.

ABSTRACTIn this work the analysis of the plasmid presence on soil aerobic cultivable heterotrophic bacterial communities was carried out checking a panel of 1,200 isolates, in order to establish the frequency of plasmid presence as well as the degree of plasmid flow between strains affiliated to the same or different taxon. Bacterial communities were isolated from two different sites of a 13-year experimental field with a clay-silt texture. Plasmid molecules were detected at low frequency (27 isolates, 2%) with a size ranging between 2 Kb and 40 Kb. The RAPD analysis performed on the plasmid-harboring isolates and the phylogenetic analysis of the whole community using the 16S rRNA gene sequences revealed the existence of transfer of the same plasmids between strains belonging to the same species and, in some cases, to different species of the same genus. As it might be expected, even though the viable cells title did not differ significantly between the two samplings, the overall data disclosed an uneven distribution of both species and plasmid-harboring strains.